Polyester film

Abstract

A polyester film having an opaque first polyester layer having an optical density greater than 2.0 and a second white polyester layer, wherein the film is made by coextrusion. The opaque first layer preferably contains carbon black. The film is suitable for use as a base for a photographic sheet.

What is claimed is:  
     
       1. A method of producing a polyester film by coextrusion which comprises coextruding an opaque polyester first layer having an optical density greater than 2.0 and a white polyester second layer. 
     
     
       2. The method of  claim 1  wherein the first layer comprises in the range from 0.05% to 10% by weight of opacifying agent, based on the weight of the first layer polyester. 
     
     
       3. The method of  claim 2  wherein the opacifying agent comprises carbon black. 
     
     
       4. The method of  claim 1  wherein the opacifying agent has a BET surface area in the range from 20 to 300 m 2 gm −1 . 
     
     
       5. The method of  claim 1  wherein the second layer comprises in the range from 5% to 60% by weight of a whitening agent, based on the weight of the second layer polyester. 
     
     
       6. The method of  claim 1  wherein the film has a deformation index (D) of greater than 2.5%. 
     
     
       7. The method of  claim 1  wherein the film has an optical density in the range from 3.0 to 10.